lib/Transforms/Scalar/SimplifyHalfPowrLibCalls.cpp

   1 //===- SimplifyHalfPowrLibCalls.cpp - Optimize specific half_powr calls ---===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements a simple pass that applies an experimental
  11 // transformation on calls to specific functions.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "simplify-libcalls-halfpowr"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Instructions.h"
  18 #include "llvm/Intrinsics.h"
  19 #include "llvm/Module.h"
  20 #include "llvm/Pass.h"
  21 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  22 #include "llvm/Transforms/Utils/Cloning.h"
  23 #include "llvm/Target/TargetData.h"
  24 #include "llvm/ADT/STLExtras.h"
  25 #include "llvm/Support/Debug.h"
  26 using namespace llvm;
  27
  28 namespace {
  29   /// This pass optimizes well half_powr function calls.
  30   ///
  31   class SimplifyHalfPowrLibCalls : public FunctionPass {
  32     const TargetData *TD;
  33   public:
  34     static char ID; // Pass identification
  35     SimplifyHalfPowrLibCalls() : FunctionPass(&ID) {}
  36
  37     bool runOnFunction(Function &F);
  38
  39     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  40     }
  41
  42     Instruction *
  43     InlineHalfPowrs(const std::vector<Instruction *> &HalfPowrs,
  44                     Instruction *InsertPt);
  45   };
  46   char SimplifyHalfPowrLibCalls::ID = 0;
  47 } // end anonymous namespace.
  48
  49 static RegisterPass<SimplifyHalfPowrLibCalls>
  50 X("simplify-libcalls-halfpowr", "Simplify half_powr library calls");
  51
  52 // Public interface to the Simplify HalfPowr LibCalls pass.
  53 FunctionPass *llvm::createSimplifyHalfPowrLibCallsPass() {
  54   return new SimplifyHalfPowrLibCalls();
  55 }
  56
  57 /// InlineHalfPowrs - Inline a sequence of adjacent half_powr calls, rearranging
  58 /// their control flow to better facilitate subsequent optimization.
  59 Instruction *
  60 SimplifyHalfPowrLibCalls::
  61 InlineHalfPowrs(const std::vector<Instruction *> &HalfPowrs,
  62                 Instruction *InsertPt) {
  63   std::vector<BasicBlock *> Bodies;
  64   BasicBlock *NewBlock = 0;
  65
  66   for (unsigned i = 0, e = HalfPowrs.size(); i != e; ++i) {
  67     CallInst *Call = cast<CallInst>(HalfPowrs[i]);
  68     Function *Callee = Call->getCalledFunction();
  69
  70     // Minimally sanity-check the CFG of half_powr to ensure that it contains
  71     // the the kind of code we expect.  If we're running this pass, we have
  72     // reason to believe it will be what we expect.
  73     Function::iterator I = Callee->begin();
  74     BasicBlock *Prologue = I++;
  75     if (I == Callee->end()) break;
  76     BasicBlock *SubnormalHandling = I++;
  77     if (I == Callee->end()) break;
  78     BasicBlock *Body = I++;
  79     if (I != Callee->end()) break;
  80     if (SubnormalHandling->getSinglePredecessor() != Prologue)
  81       break;
  82     BranchInst *PBI = dyn_cast<BranchInst>(Prologue->getTerminator());
  83     if (!PBI || !PBI->isConditional())
  84       break;
  85     BranchInst *SNBI = dyn_cast<BranchInst>(SubnormalHandling->getTerminator());
  86     if (!SNBI || SNBI->isConditional())
  87       break;
  88     if (!isa<ReturnInst>(Body->getTerminator()))
  89       break;
  90
  91     Instruction *NextInst = next(BasicBlock::iterator(Call));
  92
  93     // Inline the call, taking care of what code ends up where.
  94     NewBlock = SplitBlock(NextInst->getParent(), NextInst, this);
  95
  96     bool B = InlineFunction(Call, 0, TD);
  97     assert(B && "half_powr didn't inline?"); B=B;
  98
  99     BasicBlock *NewBody = NewBlock->getSinglePredecessor();
 100     assert(NewBody);
 101     Bodies.push_back(NewBody);
 102   }
 103
 104   if (!NewBlock)
 105     return InsertPt;
 106
 107   // Put the code for all the bodies into one block, to facilitate
 108   // subsequent optimization.
 109   (void)SplitEdge(NewBlock->getSinglePredecessor(), NewBlock, this);
 110   for (unsigned i = 0, e = Bodies.size(); i != e; ++i) {
 111     BasicBlock *Body = Bodies[i];
 112     Instruction *FNP = Body->getFirstNonPHI();
 113     // Splice the insts from body into NewBlock.
 114     NewBlock->getInstList().splice(NewBlock->begin(), Body->getInstList(),
 115                                    FNP, Body->getTerminator());
 116   }
 117
 118   return NewBlock->begin();
 119 }
 120
 121 /// runOnFunction - Top level algorithm.
 122 ///
 123 bool SimplifyHalfPowrLibCalls::runOnFunction(Function &F) {
 124   TD = getAnalysisIfAvailable<TargetData>();
 125
 126   bool Changed = false;
 127   std::vector<Instruction *> HalfPowrs;
 128   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
 129     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
 130       // Look for calls.
 131       bool IsHalfPowr = false;
 132       if (CallInst *CI = dyn_cast<CallInst>(I)) {
 133         // Look for direct calls and calls to non-external functions.
 134         Function *Callee = CI->getCalledFunction();
 135         if (Callee && Callee->hasExternalLinkage()) {
 136           // Look for calls with well-known names.
 137           if (Callee->getName() == "__half_powrf4")
 138             IsHalfPowr = true;
 139         }
 140       }
 141       if (IsHalfPowr)
 142         HalfPowrs.push_back(I);
 143       // We're looking for sequences of up to three such calls, which we'll
 144       // simplify as a group.
 145       if ((!IsHalfPowr && !HalfPowrs.empty()) || HalfPowrs.size() == 3) {
 146         I = InlineHalfPowrs(HalfPowrs, I);
 147         E = I->getParent()->end();
 148         HalfPowrs.clear();
 149         Changed = true;
 150       }
 151     }
 152     assert(HalfPowrs.empty() && "Block had no terminator!");
 153   }
 154
 155   return Changed;
 156 }